The present invention relates to a semiconductor laser in general, and, particular, to a semiconductor laser including a semiconductor laser chip and at least one temperature sensor secured directly to or integrated in the semiconductor laser chip.
Semiconductor lasers are generally known, as proceeds, for example, from the publication by H. Richter, TelekomVision 7/93, Chips mit Zukunftspotentialxe2x80x9d [Chips with Future Potential], interim results of the Telekom Research Project OEIC, TelekomVision 7/93, pp. 41 through 47, which is hereby incorporated by reference herein.
The application of such a laser is described in detail in the publication by K. H. Park, xe2x80x9cFabrication and Transmission Experiments of Distributed Feedback Lasers Modules for 2.5 Gb/s Optical Transmission Systemsxe2x80x9d published in Optical and Quantum Electronics 27 (1995), 547-552. To further enhance capacity, optical carrier frequency technologies, also referred to as wavelength division multiplex systems, are increasingly being used. The output wavelength of the semiconductor lasers used in these systems must be able to be adjusted and corrected within a very narrow range. Manipulated variables used for this purpose include the externally adjusted temperature of the laser carrier, and the laser""s pumping power.
At a constant pumping power, an incorrect determination of the temperature of the laser chip leads to deviations in the output wavelengths, particularly when it is necessary to change the pumping power for operational reasons. The reasons for a change in pumping power can be unplanned, such as the effects of ageing on the laser, or also planned, such as changing the laser""s output power in response to a change in path attenuation, or subsequent to a reconfiguration in switched networks (routing, equivalent line circuit).
While in telecommunications lasers the emphasis is on a monomode characteristic and a small line width, as well as a rapid modulability, for purposes such as material processing, it is important that the semiconductor laser have a high power output. In comparison to telecommunications lasers, high-performance lasers are often very long (up to 2 mm). Unavoidable irregularities due to manufacturing, along the active laser zone, lead to local temperature peaks, particularly in operations entailing the highest power outputs. Such irregular temperature distribution results in a diminished output power and, in the extreme case, to irreversible degradation of the laser.
In known methods heretofore, a laser""s temperature is only measured at one location, namely at its laser carrier being used as a heat sink. When measuring the temperature, errors can occur due to the heat transfer resistance between the laser chip and the heat sink, and also due to the finite thermal conductivity of the laser chip material; in addition to this such errors are caused by other heat sources produced by the bulk resistances in the pumping current""s circuit path. Besides the steady-state temperature measuring errors, large time constants also result, which adversely affect temperature control. In known methods heretofore, irregularities in the temperature characteristic were not recorded at all in the case of high-performance lasers. German Patent No. DE 19 546 443 and European Patent No. EP 0 779 526, which are hereby incorporated by reference herein, describe an optical and/or electro-optical connection, and a method for manufacturing such a connection for two optical and/or electro-optical components. FIG. 7 of European Patent No. EP 0 779 526, in particular, shows how a pump-current lead wire is secured in a semiconductor laser, and provides details of the same in the corresponding description. It also describes how a hole can be bored into a laser chip using laser welding light.
Other laser chips or semiconductor laser modules are fundamentally described in German Patent No. DE 42 32 326 and in German Patent No. DE 42 32 327.
As noted above, it is customary for the temperature of a laser to be measured at only one location, namely at its laser carrier being used as a heat sink.
An object of the present invention is to provide an arrangement of a temperature sensor or of a plurality of temperature sensors, which will enable a more precise and/or locally resolved measurement of the operating temperature, it also being possible to implement a precise temperature adjustment with substantial accuracy and/or local selectivity.
The present invention provides a semiconductor laser including a semiconductor laser chip and at least one temperature sensor disposed directly on or integrated in the semiconductor laser chip for measuring an operating temperature. A very high precision, not attainable in known methods heretofore, is achieved by securing one or a plurality of temperature sensors directly onto the laser chip, and in intimate connection with the same, in a welding operation using Nd-YAG laser light or light having similar properties. The fine temperature adjustment is advantageously carried out using Peltier elements, the components of the Peltier elements being applied directly to the laser chip using Nd-YAG laser light. In accordance with the present invention, the wavelength of the laser chip is measured and, when necessary, the wavelength of the laser chip is also adjusted, the telecommunications lasers having one measuring point per active laser zone, and the high-performance lasers having a plurality of measuring points per laser chip along the active laser zone.
Other advantages, features, and possible applications of the present invention are revealed below.